Ion extraction from magnetically driven shunting arc and estimation of ion density at sheath boundary

Ion density of a magnetically driven shunting arc discharge is estimated from the target voltage characteristics of the pulse modulator circuit in plasma-based ion implantation (PBII). The voltage recovery time constant directly reflects the ion sheath characteristics, and the sheath resistance is related to the ion density inside the transient sheath. The measured characteristics are analyzed using an equivalent circuit of the pulse modulator in PBII. The estimated ion density decreases from 3 × 108 to 4 × 107 cm− 3 with time after the arc ignition from 100 to 400 μs. This characteristic almost agrees with that of an ion current extracted from the arc plasma by applying a negative pulse voltage to the target.